This randomized controlled trial investigates the effects of hot spring balneotherapy on central fatigue elimination in adolescent rowers undergoing altitude training at approximately 1600 meters (Tengchong, Yunnan). Thirty adolescent athletes (aged 12-16 years) will be stratified by sex and randomly allocated to three groups: Group A (natural recovery, no immersion), Group B (38°C pure water immersion), and Group C (38°C sodium bicarbonate hot spring immersion). Interventions will be administered 3 times per week for 4 weeks. The primary outcomes are central fatigue indices including voluntary activation (VA) and central activation ratio (CAR). Secondary outcomes encompass cognitive function (Stroop test, Psychomotor Vigilance Test), cerebral hemodynamics (functional near-infrared spectroscopy, transcranial Doppler ultrasound), exercise performance (maximal oxygen uptake, 1000m test, 500m test), blood lactate, and hematological parameters (white blood cells, neutrophils, platelets).
Altitude training induces central fatigue characterized by decreased descending neural drive from the brain to skeletal muscle, reduced voluntary activation, and impaired cognitive function. This study employs a stratified randomized block design to evaluate whether post-exercise hot spring immersion can accelerate central fatigue recovery compared to pure warm water immersion and natural recovery. All participants will undergo standardized rowing training at approximately 1600 meters altitude. Group C will receive immersion in natural hot spring water at 38°C for 20 minutes. Group B will receive immersion in pure water at the same temperature and duration as a thermal control. Group A will undergo standard training recovery without immersion. The study incorporates partial blinding: Groups B and C are single-blinded to participants (identical appearance and protocol); Group A serves as an open-label control. Assessments will be conducted at baseline (pre-altitude), mid-intervention (Week 2), end-intervention (Week 4), and follow-up (1-2 weeks post-altitude).
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
TREATMENT
Masking
SINGLE
Enrollment
27
Standard post-exercise recovery without water immersion. Participants rest passively in a thermoneutral environment (24°C, 50-60% humidity) for 20 minutes with ad libitum water and optional self-directed stretching. No heat, cold, or hydrotherapy interventions are applied.
After exercise, full-body immersion in daily tap water. Temperature: 38°C ± 0.5°C. Duration: 20 minutes per session, 3 times per week (Tuesday, Thursday, Saturday at 16:00), for 4 consecutive weeks (total of 12 sessions). Protocol: Full-body immersion below the neck for 20 minutes, followed by a 10-minute rest before leaving the facility.
After exercise, full-body immersion in natural hot spring water (pH approx. 7.4, Na+ 1210 mg/L, HCO3- approx. 3300 mg/L, total dissolved solids \>1000 mg/L). Temperature: 38°C ± 0.5°C. Duration: 20 minutes per session, 3 times per week (Tuesday, Thursday, Saturday at 16:00), for 4 consecutive weeks (12 sessions total). Protocol: Full-body immersion below the neck for 20 minutes, followed by a 10-minute rest before leaving the facility.
Macao Polytechnic University
Macao, Macao, China
RECRUITINGVoluntary Activation
Voluntary activation assessed by the interpolated twitch technique (ITT) during maximal voluntary contraction (MVC) of the quadriceps femoris using percutaneous electrical stimulation. A single stimulus is superimposed on MVC; VA is calculated as: VA = (1 - superimposed twitch force / potentiated resting doublet force) × 100%. Higher VA indicates greater central neural drive. Unit: percentage (%).
Time frame: Baseline (Week 0), Week 2, Week 3, Week 4 (post-intervention), Follow-up (Week 1-2 post-altitude)
Central Activation Ratio
Central activation ratio measured as the ratio of maximal voluntary contraction force to the force evoked by supramaximal electrical stimulation of the femoral nerve during quadriceps contraction. CAR = MVC force / (MVC force + superimposed twitch force). Values closer to 1.0 indicate less central fatigue. Unit: ratio (0-1, no units).
Time frame: Baseline (Week 0), Week 2, Week 3, Week 4, Follow-up (Week 5-6 post-altitude)
Stroop Test Performance
Computerized Stroop Color-Word Test measuring executive function and cognitive inhibition. Outcome variables: reaction time (ms) for congruent and incongruent trials, with interference effect calculated as incongruent minus congruent reaction time. Administered in a quiet, temperature-controlled room (22-24°C). Unit: milliseconds (ms).
Time frame: Baseline, Week 2,Week 4, Follow-up (Week 1-2 post-altitude)
Cerebral Oxygenation
Changes in oxygenated hemoglobin (HbO2) and deoxygenated hemoglobin (Hb) in the prefrontal cortex during rest and cognitive tasks, measured by functional near-infrared spectroscopy (fNIRS) with a multichannel system. Outcome: relative concentration changes (ΔμM) in HbO2 and Hb from baseline. Unit: micromolar (μM).
Time frame: Baseline, Week 2, fellow up
Psychomotor Vigilance Test
5-minute Psychomotor Vigilance Test measuring sustained attention and psychomotor vigilance. Outcome variables: mean response time, and number of lapses (reaction time \>500 ms). Administered via standardized software on a tablet/computer in a quiet environment. Unit: milliseconds (ms).
Time frame: Baseline, Week 2, Week 3, Week 4, Follow-up (Week 1-2 post-altitude)
Maximal Oxygen Uptake (VO2max)
Maximal oxygen uptake measured during a graded exercise test on a rowing ergometer using a portable metabolic cart. Protocol: incremental ramp test (starting at 100W, increasing 20W every 2 minutes) until volitional exhaustion. Unit: mL/kg/min.
Time frame: Baseline (Week 0), Follow-up (Week 5-6 post-altitude)
White Blood Cell Count (WBC)
Total white blood cell count measured from fasting venous blood sample using automated hematology analyzer. Unit: 10\^9 cells per liter (10\^9/L).
Time frame: Baseline, Week 2, Follow up (Week 5-6 post-altitude)
Neutrophil Count (NEUT)
Absolute neutrophil count measured from fasting venous blood sample using automated hematology analyzer. Unit: 10\^9/L. Baseline, Week 4 11 Platelet Count (PLT) Platelet count measured from fasting venous blood sample using automated hematology analyzer. Unit: 10\^9/L.
Time frame: Baseline, Week 2, Follow-up (Week 5-6 post-altitude)
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